1. Field of the Invention
The present invention relates to a connector with built-in electronic circuit board, which is suitable for a sensor that outputs a weak signal, such as a gas sensor.
2. Description of Related Art
Japanese Patent Application Laid-open No. 2000-171435 describes a connector incorporating a control circuit board of a sensor. Such a connector enables disposing the control circuit board of the sensor between the sensor and a control device. The control circuit board on which electronic parts are soldered is mounted on a connector case of the connector connected with a cable to be connected to the sensor, and sealed by a lid or the like.
When the sensor is a gas sensor that outputs a weak signal, such as an NOx sensor or a PM sensor, it is preferable to dispose the control circuit of the sensor in the vicinity of the sensor. However, since the temperature in the vicinity of an exhaust pipe on which the gas sensor is mounted is high (approximately 125 degrees C.), when the control circuit board is a resin board, there is a concern that the solder joint portions between the control circuit board and the electronic parts cannot withstand thermal stress.
Further, when the gas sensor is provided with a heater, since the control circuit for controlling the heater generates heat, a heat dissipation structure has to be provided in the gas sensor. Further, the gas sensor has to be resistant to external radio waves because it outputs a weak signal, and also has to be water and air proof because it is mounted under the floor of a vehicle body.
Hence, such a control circuit board must be resistant to high temperature, such as a ceramic board.
However, since the ceramic board is expensive, the manufacturing cost of such a gas sensor has been high.